The ["target"] DNA is mixed into a vial of bacteria, which is then put into a custom-made machine designed in Church's lab. In the machine, the mixture is subjected to a precisely choreographed routine of temperature and chemical cycles that encourage the bacterial cells to take up the foreign DNA, swapping it into their genomes in place of the native piece it resembles. The single-stranded pieces of DNA are thought to "fake out the cell's DNA replication machinery, sneaking in and filling a gap" during the replication process, says Church. Each generation of the rapidly reproducing bacteria takes up more of the foreign DNA, ultimately producing a population that has all the desired genetic changes.